This means:
“A cardiologist supposedly identifies one particular exercise as the most important exercise for lowering the risk of a heart attack.”
Breakdown
“A cardiologist reveals” = uses the authority of a heart specialist to make the claim sound medically authoritative.
“Number one exercise” = suggests there is one exercise that is superior to all others.
“Prevent a heart attack” = implies that doing this exercise can prevent heart attacks.
Important point
The phrase “number one” is misleading. There isn’t one exercise proven to prevent all heart attacks. Regular aerobic activity, such as brisk walking, cycling, swimming, or similar activities, can improve cardiovascular fitness and reduce cardiovascular risk. Strength training also provides important health benefits.
The best exercise is generally one that is appropriate for your fitness and health level and that you can do consistently.
A more accurate version:
“Which types of exercise can help lower your risk of heart disease and heart attack?”
